Tarsal formula is the number of segments of the tarsi, which has 3 numbers a-b-c, starting with the

fore leg A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial ( anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead ...

(a), then the middle leg (b), then the hind leg (c). For example, a tarsal formula of "5-5-4" as found in the

Trictenotomidae The Trictenotomidae are a small family of beetles in the superfamily Tenebrionoidea, containing fifteen species in two genera. Most species are found in the Oriental realm where they live in montane forest habitats. The family is considered, bas ...

means there are 5 segments in the fore leg's tarsi, 5 segments in the middle leg's tarsi, and 4 segments in the hind leg's tarsi. This character is especially useful at family rank and higher.

References

Insect anatomy {{insect-anatomy-stub